The invention relates to a device for obtaining signals to be applied to the control unit of an electronic fuel injection system of an internal combustion engine from a tachometer for measuring the engine speed and a gauge for measuring the air flow supply to the engine or the intake air pressure.
Electronic fuel injection system for internal combustion engines, in various embodiments and operating on various principles, are well known. For example, articles in the Motortechnische Zeitschrift 34 (1973) 1, page 7, and 4, page 99, describe electronic gasoline injection systems operating with an airflow gauge, where the control unit is supplied with rotational speed signals obtained from ignition impulses of the engine. Articles in the Automobilitechnische Zeitschrift 72 (1971) 4, page 125; Bosch Technische Berichte 2, No. 3, November 1967, page 107; and Bosch Technische Zeitschrift 3, No. 1, November 1969, page 3, describe fuel injection systems in which the rotational speed signals are obtained by means of additional contacts on the ignition distributor. In the fuel injection systems according to the references first mentioned, the control unit forms the quotient of the airflow measurement and the speed signal to obtain a signal proportional to the injection time. However, in the systems described in the articles last mentioned, the speed is only a correction factor.
Certain vehicles equipped with fuel injection have unexplained lengthwise vehicle vibrations that appear under some operating conditions, for example in the engine brake mode or under partial load. Even more mysteriously, this vibration tendency does not occur in all vehicles of the same type and occurs in different degrees among vehicles of the same type.
As has been learned, short-term variations in the speed of the engine, such as positive or negative speed variations or irregularities, due to various causes, as for example unevennesses in the roadway or even electrical interference in the ignition from the outside, may cause changes in the injection time by way of the speed feedback in the fuel injection control unit. This leads in turn to fluctuations in the torque delivered by the engine, because of changes in the proportion of air. The extent to which such fluctuations in delivered torque manifest themselves by longitudinal vibration of the vehicle depends among other things on the elasticity in the drive train of the vehicle and, hence, on its natural frequency.